Mechanical Air Conditioning and Refrigeration is accomplished by continuously circulating, evaporating, and condensing a fixed supply of refrigerant in a closed system. Charging or recharging an Air Conditioning or Refrigeration system with refrigerant is done through the low side suction intake fitting with the use of manifold gauges and service hoses. There are several types of refrigerants used and some can be charged as a vapor and others must be charged as a liquid.
For example, R-410A is replacing R-22 refrigerant. R-410A is a mixture of HFC-32 and HFC-125, and is thus considered to be zeotropic. Zeotropic refrigerants such as R-410A must be charged as a liquid from a canister due to the possibility of fractionation of the blend of refrigerants it contains. The range of temperatures at which components in the blended components of R-410A refrigerant boil (temperature glide) is <0.3° F., making it a near-azeotropic refrigerant mixture.
Since the two components of zeotropic refrigerants such as R-410A have different boiling points, the components fractionate during boiling. That is, as the temperature increases, the lower boiling point components vaporize first. The vapor thus has a higher concentration of the lower boiling components than the liquid, and a lower concentration of the higher boiling components. When such a fluid blend is stored in a closed container in which there is a vapor space above the liquid, the composition of the vapor is different from the composition of the liquid. If the fluid is then removed from the container to charge an air conditioning system, for example, fractionation can take place, with accompanying changes in composition. Such changes can cause a refrigerant to have a composition outside of specified limits, to have different performance properties or even to become hazardous, such as by becoming flammable.
R-410A must be liquid charged into the low side of the system, so the components in the blend do not separate. Charging by weight is the preferred method of admitting the liquid charge. To accomplish this, most R-410A refrigerant cylinders must be inverted, or turned up-side-down, to allow liquid refrigerant to flow freely from the cylinder. A charging manifold valve and services hoses are used to connect the refrigerant cylinder to the system. However, assurance that no liquid is entering the system is essential for proper charging and to avoid damaging the compressor.